Is expiation (kaffarah) obligatory for a husband who ran over a person who was later found to have been injured in another accident, given that he does not know whether the victim died before or because of being run over? And is it permissible for the wife to fast the expiation on his behalf due to his inability to fast? And is it necessary to offer condolences to the deceased's family after they threatened the husband?

Your husband is not obligated to pay expiation (kaffarah (definition)) or blood money (diyah) unless it is proven that he was the killer, as the basic principle is the acquittal of responsibility. The medical report and the details of the accident should be consulted to determine the cause of death and the extent of his negligence. If diyah becomes obligatory, it is to be paid by the 'Aqilah (male agnates). The expiation is the freeing of a slave, or fasting for two consecutive months, and no one can fast on his behalf as long as he is alive. It is prescribed to offer condolences to the family of the deceased.